Year

1995

Degree Name

Doctor of Philosophy

Department

Department of Mechanical Engineering

Abstract

One of the main causes of the cavitation damage is due to the impingement of the micro-liquid jets of water generated by the collapse of the vapour bubbles. The impacts of micro-liquid jets give rise to a very high pressure pulse on the surface. These continuous impacts, initiated from many bubbles, will lead to surface fatigue and eventually fracture will occur.

In this research a boundary integral method is developed and applied to investigate the dynamics of the flow around a cavitation bubble and a bubble generated by a high local energy input in the following situations:
• a bubble in an infinite liquid domain;
• a bubble in the vicinity of a rigid boundary;
• a bubble beneath a free surface; and
• a bubble near compliant surfaces.

In the study of an isolated bubble, the behaviour of a constant pressure vapour bubble is investigated and is comparied with the behaviour of a vapour bubble with a changing internal pressure and also with the behaviour of an ideal gas bubble with different polytropic indices.

The behaviour of a constant pressure vapour bubble and also a rebounding bubble is determined in the vicinity of a rigid boundary. The influence of the buoyancy forces and the Bjerknes attraction force through the rigid boundary is discussed in detail.

In the study of a bubble beneath a free surface, the dynamics of a constant pressure bubble and also a rebounding vapour bubble is carried out under the influence of the Bjerknes force through the free surface. In this case the behaviour of the bubble by eliminating the influence of the buoyancy forces and also the behaviour of a buoyant bubble are investigated.

In the study of a vapour bubble near compliant surfaces the computation involves three domains: the vapour and/or non-condensable gases inside the cavity bubble, the flow of the surrounding water and the deformation of the compliant surface.

.An unsteady non-linear equation relates the loading to the deformation of the compliant surface. It allows the dynamic loading on compliant surfaces to be evaluated.

This computer technique depicts various modes of bubble's collapses on compliant surfaces. Significant damping effects on the micro-liquid jet momentum is obtained.

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